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Printed microelectrodes for detection of neurotransmitters from cells

Emerging printed electronics technologies posses a high potential for fabrication of cheap disposable sensors for biological applications. In this technical note we present a printed disposable system for recording neurotransmitter release from individual cells.

Single vesicle release on a printed carbon microelectrode (schematics)

Alexey Yakushenko, Jan Schnitker, and Bernhard Wolfrum

Article appeared in: Anal. Chem., 2012, 84 (10), pp 4613–4617

Published: April 18, 2012

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Techniques for monitoring vesicular release of neurotransmitters can be used to investigate processes related to chemical signal transduction between neurons or neuron-like cell lines. Diverse electrochemical methods are particularly suited to detect readily oxidizable neurotransmitters such as dopamine, adrenaline, and serotonin. Single vesicle release of neurotransmitters has been intensively studied using amperometric techniques. In amperometry, the potential of the working electrode is kept constant against a reference electrode, namely, above or below the redox potential at which the molecule of interest is oxidized or reduced, respectively. The technique has the advantage of high temporal resolution and sensitivity while lacking selectivity toward different molecules with similar redox potentials. The working electrode of choice for such measurements is usually a carbon-fiber microelectrode, which exhibits a wide potential window and inert electrochemistry. On the other hand, carbon microelectrodes cannot be easily integrated on a chip for direct cell culturing. Planar metal microelectrodes, which are extensively used for measurements of electrical activity of cells in the neurophysiological community, are, however, more prone to chemical fouling after prolonged exposure to electrolytes and have a narrower potential window that limits their application. Nevertheless, metal electrode arrays enable direct cell culture growth and in vitro detection of single vesicle release. Fabrication of these microelectrodes requires optical lithography or similar clean-room technologies for fabrication. This makes the production cost of planar microelectrode arrays (MEA) relatively high. Commercially available 64 channel MEAs are sold for more than $100 per chip. After long exposure times to electrolyte solution, the performance of the chip degrades due to electrode or passivation deterioration. According to our experience with MEAs, a typical chip cannot be reused more than approximately 5 times in long-term cell culture experiments of several weeks. For this reason, the use of low-cost disposable systems is desirable for high-throughput cell culture analysis. In this technical note, we present single-vesicle release recordings from a catecholamine-containing PC12 (rat pheochromocytoma) cell line cultured directly on a disposable screen-printed carbon paste microelectrode. The carbon paste microelectrode fabrication process is carried out in a standard chemical laboratory with no special clean-room equipment. Total material cost of a single device with all required components amounts to approximately 20 cents per chip. Additionally, the microelectrode fabrication process including first in vitro dopamine recordings from PC12 cells can be achieved in less than 6 h.

(left): Spontaneous dopamine release from PC12 cells. Vertical lines indicate the time when the applied potential was switched from 1 to 0 V and back. (right): Stimulated dopamine release from PC12 cells upon depolarization with a high extracellular KCl concentration.